COMMERCIAL FERTILIZERS 213 



toes heavily manured with nitrate of soda make a 

 luxuriant growth of vines but produce only a few 

 small tubers. When a medium dressing is used along 

 with potash and phosphoric acid, a more balanced 

 growth is obtained, and a better yield is the result. 



Heavy applications of nitrate of soda produce a rank 

 growth of straw, with a low yield of grain. The ex- 

 cessive amount of nitrogen causes the mineral matter 

 to be utilized for straw production and leaves only a 

 small amount for grain production. When applica- 

 tions of commercial fertilizers aro too heavy, plants 

 take up unnecessary amounts of food and fail to make 

 good use of it. In fact crops may be overfed or fed, 

 an unbalanced ration, the same as animals. Hence 

 in the use of fertilizers excessive or unbalanced appli- 

 cations are to be avoided. 



291. Fertilizing Special Crops. There are crops 

 which need special help in obtaining some one ele- 

 ment, and in the use of fertilizers it should be the 

 rule to help those crops which have the greatest diffi- 

 culty in obtaining food. When the soil does not show 

 a marked deficiency in any one element, light dress- 

 ings of special purpose manures may be made to the 

 following crops : 



Wheat. Nitrogen first, then phosphoric acid. 



Barley, oats, and rye require manuring like wheat, 

 but to a less extent. Each crop has a different power 

 of obtaining nitrogen. Wheat requires the most help 

 and barley and rye the least. 



